This invention relates to improvements in apparatus for dispensing finely divided powders or granular materials and, in particular, to improvements in xerographic toner dispensing apparatus.
More specifically, this invention relates to a xerographic toner container having dispensing means associated therewith that is particularly adapted for use in conjunction with a xerographic developing apparatus. Basically, in the art of xerography, a plate formed of a photoconductive surface carried on a conductive substrate is uniformly charged and the surface of the plate then exposed to a light image of an original which is to be copied. The photoconductive layer becomes conductive under the influence of the light image to selectively dissipate the charge found thereon thus forming a latent electrostatic image. To make this latent image visible, a finely divided pigmented resin-based material, commonly referred to as toner, is first charged to a potential opposite to that of the latent electrostatic image and then while still in a charged state, brought into contact with the latent image where the charged toner particles are attracted to the image where the charged toner particles are attracted to the image areas. The developer image is usually transferred from the plate surface to a final support material and fixed thereto to form a permanent record of the original.
The resin-based toners employed in the practice of the xerographic process are generally blended from finely sub-divided materials to yield an extremely fine powder composition having an average particle size of about 10 microns. As used in most automatic xerographic reproducing apparatus, the fine toner particles are brought into rubbing contact with a triboelectrically remote and relatively coarser "carrier" material. The rubbing or mixing action causes the toner particles to become triboelectrically charged to a polarity opposite that of the carrier. The charged toner particles electrostatically coat themselves on the surface of the coarser carrier material and remain bonded there in a charged state. The two component material is then brought into contact with an image bearing photoconductive plate by one of several known techniques where the toner is electrostatically transferred from the carrier surface to the latent image areas to effect development. As can be seen, the coarser carrier particles not only provide a means for charging the toner material, but also provide a vehicle by which the toner particles, but also provide a vehicle by which the toner particles are conveniently handled and transported in the xerographic development apparatus.
In order to substain continuous operation in an automatic device, the toner material consumed in the development process must be periodically replaced within the development system. One arrangement for resupplying spent toner involves the use of a sealed toner cartridge or package which is placed into the xerographic machine when toner is depleted. The package usually includes a series of openings which are covered with an easily removable adhesive strip. The strip is removed from the package while maintaining the opening in the package at a 12 o'clock position. The package is then inserted into a receiving portion of the machine generally above the developer sump and rotated to bring the openings to the 6 o'clock position. This dumps the entire contents of the package into a dispensing hopper from whence a controllable amount of toner is periodically added to the development system in accordance with an error signal developed in accordance with well known techniques. The package is left in the machine until a new package is needed to fill the hopper.
Dispensing of toner from the hopper of the above described arrangement may be accomplished by means of a toner dispensing foam roll in accordance with U.S. Pat. No. 3,596,807 or Re. 27,876.
However, it has been found that the apparatus referred to in the above identified patents while solving the problems heretofore associated with the prior art dispensing devices, has not proven entirely satisfactory for dispensing all types of electroscopic toner powder. The minute electroscopic toner powder which is contained in the dispenser, due in part to its electroscopic nature, has a tendency to form a bridge above the dispensing roller. The roller will dispense the toner powder adjacent to its surface but due to the bridging action of the toner powder, once this toner material has been removed the dispenser will cease to function. Therefore, it is necessary for the continuous functioning of the dispensing mechanism to prevent the formation of the toner powder bridge adjacent the dispensing roll to thereby ensure uniform and accurate distribution of the toner powder and continuous movement through the roll.